This invention refers to a device and a method for counteracting injury to a person sitting in a seat in vehicle, primarily a so called whiplash injury, which can occur due to a rapid change in velocity, such as a collision, primarily from the rear, or similar.
A whiplash injury is a soft tissue injury which can occur on account of violent acceleration and/or deceleration applied to the cervical spine. The classic case where these kinds of neck injuries occur is when sitting in a car which is subjected to a rear-end impact, but can also occur in other activities than car driving, such as in participating in certain sports.
According to the Folksam insurance company, 16,000 claims are sent to the insurance companies every year because o rear-end impacts in Sweden alone. Of these cases, 1,500-2,000 sustain permanent injury and 100-200 have to be given a disability pension. Whiplash injury is the most common type or injury resulting in compensation from the insurance companies. When head restraints, popularly termed head rests, became standard in cars, there were considerable hopes that whiplash injuries would disappear. The disappointing result was that the risk of permanent injury only fell by less than 20%, which shows that the problem largely remains.
Several researchers agree that the following factors and situations are of decisive importance for the question of whether a collision will cause whiplash injury or not.
The distance between the head and the head restraint, and the vertical location of the head restraint.
The magnitude of the collision, the crash pulse.
The stiffness of the car. A stiff car gives greater acceleration, and thus higher forces.
The angle of the backrest.
The muscular strength of the individual, in combination with the length of the cervical spine.
If the person is prepared, and tensions his neck muscles back against the head restraint before the collision, the risk of whiplash injury is minimal.
Small children who travel in rearwards-facing child seats are subjected to the same or greater forces in a front-end crash than adults who are subjected to a rear-end collision. Despite this, children seldom suffer from neck injury in a front-end collision. Children very seldom sustain whiplash injuries.
Women are subjected to about a 50% greater risk than men of suffering whiplash injury in a rear-end collision. Statistics from the same type of car (Folksam).
It has been found that the injury frequency is lower in older cars, where the seat backrest collapses in a rear-end collision, compared with newer cars with stronger seats (VTI).
People in the back seat are only subject to half the risk of sustaining neck injuries compared with people in the front seat. This is despite the fact that head restraints are frequently not provided for the rear seats. (Folksam).
xe2x80x9cBouncyxe2x80x9d seats entail a greater risk of whiplash injury (Chalmers University of Technology).
About 25% of all whiplash injuries occur in front-end collisions (Folksam).
Passengers in a 4-door Volvo 240 have a 20% higher incidence of whiplash injury compared to passengers in a car which is identical, except that. it only has 2 doors. The only difference is that on the 2-door car, the B pillars are located 270 mm further back, compared with the 4-door model. This affects the position of the upper seat belt anchorage (Folksam).
The last five points indicate that the risk of sustaining a whiplash injury are greatest when the head is thrown forwards as far as it will go (hyperflexion), which occurs after about 400 ms. Regardless of when the injury occurs, the risk is considerably reduced if the acceleration of the seat is minimized.
In recent years, research in this area has been intensified, which has led to new theories and experience related to the cause of whiplash injury. Several theories and initiatives have been found to be incorrect and have therefore now been rejected. This means now that there are old technical solutions which do not solve the problem.
Since the person sits completely still at the start of the crash sequence, the solution should be based on a system or device which reduces the acceleration to less than 4 g, since it has been found that whiplash injury is avoided at accelerations below 4 g. This has been demonstrated in experiments on volunteers (please refer to xe2x80x9cComparison of head-neck kinematics during rear-end impact between standard Hybrid III RID neck, volunteers and pmtosxe2x80x9d) By allowing the entire seat to move backwards on a sledge-like element in the car during the instant of collision, the acceleration can be reduced to less than 4 g. Through lower acceleration, lower forces are experienced, which leads to a strongly reduced risk of injury.
In crash tests performed by the VOLVO Car Corporation (VOLVO Technology Report on. 2, 1996), acceleration and velocity values in a typical rear-end collision were found to have the values shown in diagrams 1 and 2.
FIGS. 3-8 show the crash sequence in the first 400 milliseconds, where FIG. 3 shows the crash sequence at time 0 milliseconds (ms), where the person is in the initial position and is thus not affected by any acceleration due to collision etc. FIG. 4 shows the crash sequence at a time of 50 ms, when the acceleration has reached its peak after only 10 ms. The speed of the car increases more or less linearly and has reached its top speed after about 50 ms on account of the collision. The body initially moves straight backwards without any mutual displacement of members. At 50 ms, the person""s neck muscles begin to tense in a reflex action to counteract the rearwards movement of the person""s head. This is regarded as being a decisive factor when the sequence is studied. All studies involving acceleration greater than 5 g have been a cone on dummies, cadavers etc. FIG. 5 shows the crash sequence at a time of about 100 ms, when the relative movement begins. The shoulders stop and the head and lower body continue to move backwards. This has been proven by researchers at the Chalmers University of Technology and others. They found that this is because the backrest is stiffer at the top, due to the cross beam in the backrest frame which unites the right and left sides of the backrest. At the same time, the mass of the body is greater in the pelvic area than in the shoulder area. There are theories that whiplash injury is caused by this effect, due to the rapid increase in pressure in the cervical spinal canal, which occurs when the head moves backwards and the volume of the cervical spinal canal decreases in a very short space of time due to the extension. This leads to an increase in pressure in the cervical spinal canal which can cause bleeding in the blood vessels around the spinal canal (myelorrhagia). Experiments have been performed on pigs at Chalmers University of Technology, in which the increase in pressure in the cervical spinal canal due to forced rapid extension was measured. Another probable source of injury would be the damage caused by the shear stress in the neck, which occurs when the head wants to move back relative to the shoulders. This effect is similar to a pack of cards lying on a table when you move the upper part of the pack sideways. The cards illustrate the disks in the cervical spine. Between 100-200 ms, the neck muscles have reached their maximum force in trying to stop the rearwards movement of the head. This muscle force represents a bending moment equivalent to a force of up to 300 N at eye height. FIG. 6 shows the crash sequence at 200 ms when the head has moved back as far as it goes, relative to the backrest and head restraint. The neck muscles are still at maximum tension. The backrest and head restraint are bent back to a maximum, and like a big spring, they will soon throw the head and torso forwards with great force. FIG. 7 shows the crash sequence at 300 ms, when the head has about twice the speed of the car and seat. The neck muscles are still at maximum tension, which means that the acceleration of the head continues. It is probable that the head reaches nearly three times the speed of the car and seat when the backrest is xe2x80x9cbouncyxe2x80x9d. This is because the backrest and neck muscles interact in an unfortunate manner. FIG. 8 shows the crash sequence at about 400 ms, when the head reaches its normal stopping point. The torso suddenly stops when it meets the stiff seat belt. At this time, the head continues forwards, with considerable over-extension. Several facts indicate that it is here that the whiplash injury occurs. This would explain the whiplash injuries which occur in front-end collisions and would also explain why the incidence of whiplash injury in a 4-door Volvo 240 is higher than in a 2-door, during a rear-end impact.
From this reasoning follows the thesis that it is very important to reduce the acceleration and thus to reduce the forces in a rear-end car collision. One way to do this is to allow the entire seat to move backwards in the car, in a controlled and damped movement, where the seat remains in a rearward position.
One solution is demonstrated in WO 96/16834, which is mainly based on backrest movement. The solution lacks a trigger mechanism, whose purpose is to release the rearward movement. This gives the seat a purely linear movement, which would appear to be parallel with the floor of the car, and is only intended to delay the time until the occupant""s head contacts the head restraint. It can primarily be described as a spring which gives a forward and rearward movement. Dampers and plasticizing solutions are described, however. No linear-arctuate movement or trajectory are described. The entire solution in WO 96/16834 is based on the assumption that the occupant""s back, neck and head are not supported and will be subjected to a considerable impact with a certain delay, because of the force against the backrest, which could cause a whiplash injury. The occupant and the seat are initially at rest, with no other forces acting upon them than gravity. When the floor of the car suddenly begins to accelerate, the back and backrest are carried along as well. The present invention and the invention described in WO 96/16834 do not have the same assumption about the fundamental reasons for why whiplash injury occurs. This means that the solution presented in WO 96/16834 is intended to solve a problem which is not foreseen in this invention.
The invention in U.S. Pat. No. 3,992,0.46 is intended to reduce injury in a rear-end collision. This invention is also largely based on linear movement in parallel with the floor of the car. The invention in U.S. Pat. No. 3,992,046 and the present invention do not solve the same problem, since one refers to front-end collisions and the other refers to rear-end collisions.
The invention in WO 93/01950 is also only intended to reduce injury in front-end collisions. The invention lacks a trigger mechanism and is based on a seat track which differs from the present invention. In addition, the invention in WO 93/01950 does not remain in its triggered position after it has been triggered.
The invention in U.S. Pat. No. 3,802,737 is a totally different technical solution. In that solution, the head restraint has a higher acceleration than the floor. The present invention is based on the opposite principle, i.e. it reduces the acceleration of the head restraint. The solution in U.S. Pat. No. 3,802,737 is mainly based on deformable sections in the backrest. In that solution, the head restraint is moved backwards and upwards in the car. In the present solution, the movement is backwards and downwards, or movement backwards at the same time as the front of the seat moves upwards.
The above description of previously-known technology gives a collection of inventions which all refer to some extent to injuries sustained in collisions. Another major and important difference consists of the problems which these inventions are intended to solve. In this connection, it is important to point out that one consequence of intensified research in this field is increased knowledge about whiplash injuries and their origins, which has led to and constantly leads to new problem formulations and deeper nuances of old problem formulations. This means that there are considerable differences between current problem formulations and old ones.
The fact that the mechanisms of the car, the seat and the head restraint all interact with the neck muscles is a phenomenon which has not previously been studied in depth. Almost all studies involving acceleration greater than 5 g have been done on dummies or cadavers, which is obviously a limitation in this area. New results indicate, as noted above, that: it is the interaction between the occupant and the seat which cause whiplash injuries. The main purpose of the invention is to reduce the acceleration to which the body is subjected after the incidence of the collision to less than 4 g, since it has been found that whiplash injuries occur in collisions exceeding 5 g.
These new findings, combined with this invention, will lead to fewer injuries. The purpose of this invention is achieved through a device and a method intended to counteract the occurrence of whiplash injury to a person sitting in a seat, which could occur through a rapid change in velocity, such as in a collision essentially from the rear or similar. The characteristics of this invention are that the arrangement contains a means whereby the seat will move in a controlled manner against the direction of movement during a change in velocity, and that the seat is provided with guidance devices which are intended to give the seat and the person sitting in it an essentially simultaneous and essentially linear movement against the direction of movement and/or an essentially arcuate movement, and that the seat is arranged so that it will remain in its rearward position after the change in velocity.
When the seat moves backward, there is a risk that it will collide with a knee belonging to a rear-seat passenger. This can be reduced if the seat is given extra inclination when the device is triggered, which leads to a reduction in injury of the rear-seat passengers.
These purposes have been solved in this invention, by means of the characteristics described in the patent claims.